This was purely intended to be an emulation of the Hammond Chorus/Vibrato effect, but I always thought it would also make an interesting, more general, and stereo, chorus device.

That would be a "true analogue" chorus in a different sense than the BBD-based effects, because the signal is not sampled.

It's not free of side effects, thou. It has a somewhat rough modulation waveform, as instead of changing a delay time continuously, it interpolates between 9 taps of a 1ms analogue delay line. It's a linear interpolation, not a switching - best thing is you listen to the sound samples and decide for yourself. It's very rough (in a Hammond-ish way!) for vibrato, and increasingly smoother when the dry signal is mixed in for chorus.

It's a quite complicated method to crate a simple chorus, compared to a BBD circuit. It requires a 50-pole (fifty!) low pass filter, but that can easily be built from 25 cheap inductors (less than a dollar per piece at Mouser) and 25 capacitors.

On the positive side, it's a lot more "direct" sounding than a BBD-based (or digital delay based) chorus, as the maximum delay time thru the whole circuit is only 1ms. (Speak of latency ...)

If there's enough interest, this could be a project for a future PCB development. I wouldn't restrict this to Hammond emulation, but make a mono-in / stereo out device in the fashion of many Roland / Boss dual-BBD chorus circuits. Just without BBD. Let me know what you think ...

JH.

ETA: this is not to be confused with my Interpolating Scanner, which is planned to be a future MOTM module._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

FWIW, chorus-wise I'd be interested in something BBD-based, like your Dimension D. I have a few MN3007s lying around.

Regards,
Joe

Maybe I'll also make something BBD-based some time. But right now I'm very excited about a chorus that doesn't need any BBDs.

Don't let yourself be confused from the focus on Hammond-Vibrato emulation on my web site. I really want to explore that scanning principle for a wider range of applications. Who can say if I don't get something as subtle and unique as a Dimension D out of it, among other things?

I'm not boasting, and I don't promise anything. In fact, as I type this, I don't know what I'll get out of it. My plan to find out what is possible goes like this:

I'll make a PCB with the core functions: The 50-pole low pass filter, the multiplexers for the length selection, the multiplexers for the scanning pre-selection, the VCAs and crossfade circuit for the scanning fine-selection, the counters and VCO for the modulation. This fills a 160mm x 100mm double sided board (see picture).
This, as a standalone board, will already do the Hammond stuff and has a second output that is modulated in opposite direction, creating a Mono-in, True-Stereo-out effect like a two-BBD chorus.

Then I'll build all the extra stuff and try various things on veroboard, like:
Preset settings a la Dimension D, Acceleration and Brake functions a la Rotating speaker, and other things that come to mind.

If I find anything that I find worthy to be shared, I'll make a second PCB board with these functions and a power supply, and sell the two PCBs as a set.

Speaking of power supply: The main board works with +/-7.5V, and the second board will contain an on-board regulator, so you can connect either +/-15V DC, or 9V AC (AC Wallwart), or (and that is a first time for my circuits): a +/-12V DC voltage. I think somebody will find the 12V option useful.

JH.

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_________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

This, as a standalone board, will already do the Hammond stuff and has a second output that is modulated in opposite direction, creating a Mono-in, True-Stereo-out effect like a two-BBD chorus.

Then I'll build all the extra stuff and try various things on veroboard, like:
Preset settings a la Dimension D, Acceleration and Brake functions a la Rotating speaker, and other things that come to mind.

Ah, I wasn't aware of the vast possibilities! Now I'm looking forward to the results of your experiments!

Ah, I wasn't aware of the vast possibilities! Now I'm looking forward to the results of your experiments!

I think Hammond the organ company themselves made experiments with multiple scanners that ran on different modulation speeds for creating a more natural, church-like chorale effect. Not many of these were built, however, and I can't even remember the model numbers. But I thought it was quite impressive when someone pointed me to it some years ago. And they did it all with mechanical scanners!

My board will have two outputs that scan in opposite direction, on the same (but variable) speed (like many Roland chorus devices).
But of course it's possible to use several boards to get multiple-LFO modulations. (With some flying wires it will be possible to share the 25 inductors and caps and the buffer amps between multiple boards, so this won't be expensive either.

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

I made some more sound samples, this time with my Wurlitzer 200A for an input signal. (This is still done with my old scanner vibrato, in mono, and with rather limited control. The new one will be stereo.

At fast modulation speed, the effect can be as deep as with any BBD chorus.

The big advantage over BBDs is that the chorused sound is a lot more immediate, because of the ultra short delay:
On a BBD chorus, you set some initial delay, and then modulate the delay time up and down a little, starting from that initial delay. In the Scanner Vibrato, the modulation really goes down to zero milliseconds.

I think you can hear that in the samples when the effect is switched in and out - the sound doesn't loose its directness, it just becomes warm and modulated.

_________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

I'm curious too - I like the subtlety of the sound. Your samples remind me of a Leslie for some reason.

I wouldn't dare to advertize it as a Leslie simulator, but it has some important features in common with a Leslie:

* Sine-shaped modulation of delay time for a true doppler effect
* A lot of high audio frequency resonances (from the enclosure around the horn in the Leslie - from the non-ideal termination of the delay line in the scanner chorus)
* A linking beteen time modulation and loudness modulation.

No pan modulation though. At least not yet.
And the maximum delay time may be a little short, too - I must re-calculate that.

Quote:

Now that you have mailed out the Tau Pipe Phaser boards and tested the Frequency Shifter board, you should reward yourself and take the rest of the night off

But then there's this final Harry Potter book, and I'm only halfway through ...

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

_________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

I can make a small run of this board if there really is enough demand.

But it's just good for the Hammond kind of Vibrato. I'm not so sure I'll make a second board for this - it doesn't live up to the "universal short-delay modulation engine" I thought it might possibly be.
The stereo effect is nice, but nothing dramatic.
It's a one-trick-pony for Hammond-like effects.
It only sounds good on band-limited input signals like Hammond organs (or Hammond emulators).
You need a +/-7.5V supply for this (not included on the board).
You can omit two CD4051's and two LM394's if you don't need Stereo.
It's quite difficult to build, with many vertically mounted resistors.

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

I'd be interested in taking a look at that board and any developments that took place since that first prototype. (the links above are dead -- apparently since the crash)

Have you attempted the leapfrog filter idea beyond simulation?

--Bob

I haven't tried the leapfrog method - been afraid of noise adding up and parasitic effects being multiplied from stage to stage.

The board I prototyped works for emulating the Hammond chorus, but didn't live up to my expectations for other uses.
And there are not so many who would just want to buy a board just for Hammond Vibrato emulation, so I don't know what to do with this.
I could raise the price to make this a worthwhile effort even with just a few boards sold, but so far I just hesitate, ond focus on th eother projects in line ...

33mH inductors work with 47nF caps and 820 Ohm termination.
The losses of these tiny inductors are considerable, so I need a slightly increasing gain for the buffer stages along the line. Unity gain at the beginning, and almost x4 at the end of the line.

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

I can think of several people who would LOVE to have a Hammond-style scanner vibrato.

If you decide you don't want to sell boards, would you consider sharing your layout?

I think it'd be great to play around with.

mr coffee

Well I didn't exactly say I won't sell any boards.

The situation is this, without glossing anything over:

For what I intended this project to be, an universal delay-modulation core, it has failed.
Delay time is simply too short for this, and the on-board VCO has a flaw, such that it won't go down to slow modulation rates.

Nevertheless it works as intended for Hammond Scanner Vibrato emulation, just like my first prototype on veroboard did.
You have to connect a trimpot where the VCO input was meant to be, and set it to 412 rpm, or whatever the Hammond Sanning rate was intended to be.

One quarter of the board space is wasted on Stereo mode (well, it sounds ok in stereo, but not overwhealming), and the board is rather cramped with components (vertically mounted resistors etc).

What I do not want is making a redesign of the board.
If you want the board just as it is, and don't judge my engineering skills on it, I can probably make a small run. No big documentation like for the tau project, though. You solder in the components as printed on the board, connect inputs and outputs and switches for chorus/vibrato, and I/II/III mode, and the trimpot mentioned above. And a +/-7.5V supply, which is not (!) included on the board.

If you're still undeterred, send me a mail and write me if you would buy a board for EUR 30.00 (shipping worldwide included). Please tell me also (for the case that I only get a very small number of offers), if you'd be also willing to pay 40.00 or 50.00 . I'm not trying to squezze out the max of it. This will be low-profit in any case; I just don't want it to be entirely no-profit.

JH.

Now playing: Tangerine Dream, Phaedra_________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

I think Hammond the organ company themselves made experiments with multiple scanners that ran on different modulation speeds for creating a more natural, church-like chorale effect. Not many of these were built, however, and I can't even remember the model numbers.

believe it or not, the slower "chorale" scanner was in production for a number of years. the H-100 had two scanners and lines, vibrato and chorale.

the vibrato scanner and line were pretty much like on the 2 and 3 series organs, but the scanner was mechanically more compact.

the chorale, now this is the really cool part. the chorale was _two_ delay lines in series, with twice as many contacts on the scanner.

there are many H-100 organs in the field, and some of them even work (it mixed tubes and transistors in the same chassis, and they never built a prototype ... they just put it in production because the marketing department controlled Hammond at the time. the H-100 has the highest failure rate of any tonewheel Hammond and if you have one that doesn't work good luck. i've disassembled two of them for parts because they were unrepairable.)

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

Instead of taking another go on a dedicated chorus / vibrato module, I could offer a full-fledged Interpolating Scanner with 9 stages, with an option to have the inductors on the PCB to turn it into a Hammond Chorus/Vibrato.

That way, the PCB can be used by both, Modular Synth users, and those who are looking for a good Hammond Vibrato emulation.

So the idea is to combine the two projects, hoping there will be enough demand for such a PCB to make it a project to be in the black, commercially.

The new version would have 9 stages of linear scanning (to fully cover the 16 positions of the mechanical rotary Hammond scanner). The scan can be performed by *any* modulation source (LFO, envelopes, audio rate, you name it) - not just with a LFO as in my earlier scanner vibrato.
All the audio waveshaping capabilities of the Interpolating Scanner would be preseved, as well. (Piecewise linear interpolation of fixed, or modulated, breakpoints).

The pcb would also include the footprint for 25 inexpensive inductors, plus the buffer stages for makeup gain (required with cheap inductors; unlike the original Hammond Line Box)

All the interconnections between this inductor delay line and the Scanner part would be done mechanically, with switches, just like the real Hammond. (No more CMOS switch matrix.)
This also allows to use the board for a generic interpolating scanner with a jack for each stage's audio or CV input - with these inputs normalized to the Inductor delay line's taps.

No more SSM chips in the new version, either. VCAs will all be discrete, built from transistor pairs. (9 transistor pairs like LM394 or similar required)

Would this be an interesting project?

JH._________________"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)

I just found and joined this forum and this topic caught my eye. The idea of the inductor-capacitor line was used in a slightly different way in the Schaller Rotor Sound. I had one of these way back when and of course wish I still did!

The way it worked was to use 18 ferrite core transformers and (I'm guessing here!) modulating the apparent primary inductance via a control signal applied to the secondary (which is not in the audio path).

The sound was really good, way better than the typical phaser of the period, but the modulation system was clunky and non-linear. I always thought it had lots of potential for a leslie sim though. Lots of potential for taps too.

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